Symmetric hybrid converters

ABSTRACT

Systems and methods for power conversion are described. Symmetric topologies and modulation schemes are described that may reduce common-mode noise. For example, a system may include a transformer including a first secondary winding and a second secondary winding; a rectifier, including a set of switches, that connects taps of the first secondary winding and the second secondary winding to a first terminal and a second terminal, wherein the rectifier is symmetric with respect to the first secondary winding and the second secondary winding; a battery connected between the first terminal and the second terminal; and a processing apparatus that is configured to control the set of switches to rectify a multilevel voltage signal on the transformer, including: selecting a modulation scheme from among two or more modulation schemes based on a measured voltage level of the battery.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.16/283,935, which was filed on Feb. 25, 2019, which claims the benefitof U.S. Provisional Application No. 62/637,633, filed on Mar. 2, 2018.The content of the foregoing applications is incorporated herein byreference in its entirety for all purposes.

TECHNICAL FIELD

This disclosure relates to symmetric hybrid converters.

BACKGROUND

Multilevel power converters are used to transfer power between circuitsoperating at different voltage levels. For example, multilevel powerconverters may be employed at terminals of high voltage powertransmission lines. For example, multilevel power converters may beemployed in power supplies for computing server racks.

SUMMARY

Disclosed herein are implementations of symmetric hybrid converters.

In a first aspect, the subject matter described in this specificationcan be embodied in systems that include a transformer including a firstsecondary winding and a second secondary winding; a rectifier, includinga set of switches, that connects taps of the first secondary winding andthe second secondary winding to a first terminal and a second terminal,wherein the rectifier is symmetric with respect to the first secondarywinding and the second secondary winding; a battery connected betweenthe first terminal and the second terminal; and a processing apparatusthat is configured to control the set of switches to rectify amultilevel voltage signal on the transformer, including: selecting amodulation scheme from among two or more modulation schemes based on ameasured voltage level of the battery.

In a second aspect, the subject matter described in this specificationcan be embodied in systems that include a transformer including a firstsecondary winding, connecting a first tap and a second tap, and a secondsecondary winding, connecting a third tap and the second tap; a firstcapacitor connecting the first tap to a first node; a second capacitorconnecting the third tap to a second node; a first switch connecting thefirst node to a first terminal; a second switch connecting the firstnode to the second node; a third switch connecting the second node to asecond terminal; a fourth switch connecting the second tap to the firstterminal; a fifth switch connecting the second tap to the secondterminal; and an electrical load connected between the first terminaland the second terminal.

In a third aspect, the subject matter described in this specificationcan be embodied in systems that include a transformer including a firstsecondary winding, connecting a first tap and a second tap, and a secondsecondary winding, connecting a third tap and a fourth tap; a firstswitch connecting the first tap to a first terminal; a second switchconnecting the first tap to the fourth tap; a third switch connectingthe fourth tap to a second terminal; a fourth switch connecting thesecond tap to the first terminal; a fifth switch connecting the secondtap to the third tap; a sixth switch connecting the third tap to thesecond terminal; and an electrical load connected between the firstterminal and the second terminal.

In a fourth aspect, the subject matter described in this specificationcan be embodied in systems that include a transformer including asecondary winding connecting a first tap and a second tap; a firstcapacitor connecting the first tap to a first node; a second capacitorconnecting the second tap to a second node; a first switch connectingthe first node to a first terminal; a second switch connecting the firstnode to the second node; a third switch connecting the second node to asecond terminal; and an electrical load connected between the firstterminal and the second terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is best understood from the following detaileddescription when read in conjunction with the accompanying drawings. Itis emphasized that, according to common practice, the various featuresof the drawings are not to-scale. On the contrary, the dimensions of thevarious features are arbitrarily expanded or reduced for clarity.

FIG. 1A is a circuit diagram of an example of a system including a highvoltage to low voltage DC/DC converter.

FIG. 1B is a circuit diagram of an example of a system including amulti-stage, high voltage charger.

FIG. 1C is a circuit diagram of an example of a system including asingle-stage, high voltage charger.

FIG. 2 is circuit diagram of an example of a system including a hybridtwo-level half bridge converter.

FIG. 3A is a circuit diagram of an example of a transformer.

FIG. 3B is a circuit diagram of an example of a transformer.

FIG. 4 is a circuit diagram of an example of a system including a hybridhalf bridge converter.

FIG. 5 is a plot of an example of a modulation scheme for switches of ahybrid half bridge converter with corresponding transformer voltage andcurrent signals.

FIG. 6 is a plot of an example of a modulation scheme for switches of ahybrid half bridge converter with corresponding transformer voltage andcurrent signals.

FIG. 7 is circuit diagram of an example of a system including a hybridfull bridge converter.

FIG. 8 is a plot of an example of a modulation scheme for switches of ahybrid full bridge converter with corresponding transformer voltage andcurrent signals.

FIG. 9 is a plot of an example of a modulation scheme for switches of ahybrid full bridge converter with corresponding transformer voltage andcurrent signals.

FIG. 10 is a block diagram of an example of a system for powerconversion.

FIG. 11 is a flow chart of an example of a process for controllingswitches of a rectifier for power conversion.

DETAILED DESCRIPTION

Described herein are systems, circuits, and methods that may be used toimplement symmetric hybrid converters. Efficiency, size, weight, powerdensity, and reliability can be important design considerations in powerconverters. Power converter circuit topologies and modulation schemesare described that may increase efficiency, reduce size and weight,increase power density, and/or increase reliability compared toconventional topologies and modulation schemes. For example, these powerconverters may be implemented in power distribution networks,photovoltaic systems, wind turbines, electric vehicles, or computingserver racks.

For example, a topology of switches in an inverter connecting secondarywindings of a transformer to an electrical load may be symmetric withrespect to the secondary windings of the transformer. The symmetry ofthe topology may enable switches to be opened and closed in modulationstates that are symmetric and generate zero or small common mode noise.In some implementations, the symmetry of the topology may enableswitches to be opened and closed in one or more pairs of modulationstates that are individually asymmetric with respect to the secondarywindings of the transformer, which may result in transient common modenoise, but a pair of asymmetric modulation states are symmetric withrespect to each other and generate zero or small net common mode noisewhen the pair of states are balanced in a cadence of a modulationscheme. Using a converter topology and/or modulation scheme that issymmetric with respect to the secondary windings of the transformer mayreduce common mode noise, which may allow for an elimination orreduction in filtering used to prevent electromagnetic interferenceemanating from the magnetic components of the converter. Reducing theamount of electromagnetic interference filtering may allow a powerconverter to be constructed for less expense and/or with smaller sizethan in a converter with high common mode noise and resultingelectromagnetic interference.

In switched multilevel converters, multiple modulation states may beused for a given transformer voltage level. The multiple states for avoltage level may utilize (e.g., conduct current through) differentcomponents (e.g., switches), and alternating between the multiple statesduring operation of the converter may serve to balance the usage ofthese components. Balancing the usage of components may reduce thermalstress on components and increase reliability of a power converter.Circuit topologies and modulation schemes for efficiently implementingthis strategy are described below.

Different modulations schemes can be used for a power converterdepending on a present voltage level of a battery being charged usingthe power converter. When the battery voltage is high, a modulationscheme that splits current and/or voltage between multiple secondarywindings of a transformer. When the battery voltage is low, a modulationscheme that concentrates current and/or voltage in a single secondarywinding of a transformer at times, while balancing the usage of thesecondary windings of the transformer over multiple states in themodulation scheme.

While the disclosure has been described in connection with certainembodiments, it is to be understood that the disclosure is not to belimited to the disclosed embodiments but, on the contrary, is intendedto cover various modifications and equivalent arrangements includedwithin the scope of the appended claims, which scope is to be accordedthe broadest interpretation so as to encompass all such modificationsand equivalent structures as is permitted under the law.

FIG. 1A is a circuit diagram of an example of a system 100 including ahigh voltage to low voltage DC/DC converter. The system 100 couplespower from a high voltage battery 102 (e.g., a 400 Volt or an 800 voltbattery) to a low voltage battery 104 (e.g., a 12 volt or a 48 voltbattery). A capacitor 106 is in parallel with the high voltage battery102 and a capacitor 108 is in parallel with the low voltage battery 104.The system 100 includes a transformer 110 that couples power from aninverter 120 to a rectifier 130. For example, transformer 110 may beimplemented using the transformer 300 of FIG. 3A. For example,transformer 110 may be implemented using the transformer 350 of FIG. 3B.The high voltage battery 102 is connected to terminals of the inverter120 and the low voltage battery 104 is connected to terminals of therectifier 130.

For example, a computing server rack may use the system 100 to couplebulk power at a low DC voltage (e.g., from a battery back-up system) toindividual equipment items. For example, electric vehicles may use thesystem 100 to couple power from a high voltage battery 102, whichprovides power to a propulsion system to move the vehicle, to a lowvoltage battery 104, which provides power to one or more auxiliarysystems of the electric vehicle. For example, the propulsion system mayinclude a DC motor, a drive train, and/or a transmission systemconfigured to convert electrical power to mechanical power and transferthe mechanical power to torque on wheels of the vehicle. Someapplications utilize a high battery voltage (e.g., a 400 volt battery oran 800 volt battery) and different low voltage battery voltages (e.g.,12V and 48V) and may also support very wide input range and outputrange. On the low voltage side, to increase the power rating of theconverter, many devices may be connected in parallel, which may restrictthe practical power output of the converter.

The rectifier 130 may be suitable to be interfaced with the low voltagebattery 104 and be able to provide high efficiency while meeting desiredspecifications. For example, rectifier 130 may be implemented using thetopology of the system 200 of FIG. 2. For example, rectifier 130 may beimplemented using the topology of the system 400 of FIG. 4. For example,rectifier 130 may be implemented using the topology of the system 700 ofFIG. 7. Switching control may be formulated for operation of a topologyof the inverter 120 and the rectifier 130 to attain zero voltageswitching over an entire battery range. For example, the processingapparatus 1010 of the system 1000 of FIG. 10 may be used to implementswitching control for the system 100. Zero voltage switching enables useof switching frequency in the MHz range and may reduce the size ofmagnetic components. This may result in obtaining high power densitywhich converts to savings in volume and weight of the system 100.

For high voltage batteries (e.g., an 800 volt battery), newer multileveltopologies may be used to exploit the benefits of latest wide band-gapGaN technology (e.g., available to 650 volts). The inverter 120 may besuitable to be interfaced with the high voltage battery 102 and be ableto provide high efficiency while meeting desired specifications. In someimplementations, switching control may be formulated to achieve activevoltage balancing of split capacitors in the inverter 120. For example,the inverter 120 may include a three-level stacked half-bridge topology.The topology of the inverter 120 may achieve higher efficiency thanconventional half-bridge topologies.

The converters of the system 100 may be bidirectional in the sense thatpower may be transferred from the high voltage battery 102 to the lowvoltage battery 104 and/or from the low voltage battery 104 to the highvoltage battery 102.

The inverter 120 and/or the rectifier 130 topologies can be employed inother systems for different applications, such as the system 140 of FIG.1B and the system 160 of FIG. 1C. The inverter 120 and the rectifier 130may be bidirectional, and hence can be used in applications of highvoltage to low voltage DC/DC converters, and high voltage chargers.

FIG. 1B is a circuit diagram of an example of a system 140 including amulti-stage, high voltage charger. The system 140 includes a highvoltage battery 142 that is charged from an alternating current (AC)power source 144 (e.g., from a grid). A capacitor 146 is in parallelwith the high voltage battery 142. Power from the AC power source 144 isconverted to DC voltage using the rectifier 150. Power from theresulting DC voltage across a capacitor 152 may then be the furtherconverted to a DC voltage level used to charge the high voltage battery142 by a DC/DC converter including the inverter 120, the transformer110, and the rectifier 130.

FIG. 1C is a circuit diagram of an example of a system 160 including asingle-stage, high voltage charger. The system 160 includes a highvoltage battery 162 that is charged from an alternating current (AC)power source 164 (e.g., from a grid). A capacitor 166 is in parallelwith the high voltage battery 142 and a capacitor 168 is in parallelwith the AC power source 164. Power from the AC power source 144 isconverted to a DC voltage level used to charge the high voltage battery162 by an AC/DC converter including an AC/AC converter 170 that couplesa high frequency multilevel signal through the transformer 110 to therectifier 130.

FIG. 2 is circuit diagram of an example of a system 200 including ahybrid two-level half bridge converter. The system 200 includes atransformer 210 including a secondary winding 212 connecting a first tap214 and a second tap 216; a first capacitor 220 connecting the first tap214 to a first node 244; a second capacitor 222 connecting the secondtap 216 to a second node 246; a first switch 230 connecting the firstnode 244 to a first terminal 240; a second switch 232 connecting thefirst node 244 to the second node 246; and a third switch 234 connectingthe second node 246 to a second terminal 242. The system 200 includes anelectrical load 250 connected between the first terminal 240 and thesecond terminal 242. The electrical load 250 may include a battery(e.g., a 12 Volt, a 48 volt, a 400 volt, or an 800 volt battery). Thesystem 200 includes a capacitor 252 in parallel with the electrical load250. For example, the system 200 may be implemented as part of thesystem 100 of FIG. 1A. For example, the system 200 may be implemented aspart of the system 140 of FIG. 1B. For example, the system 200 may beimplemented as part of the system 160 of FIG. 1C.

The system 200 includes a transformer 210 including a secondary winding212 connecting a first tap 214 and a second tap 216. In someimplementations (not shown), the transformer 210 may be replaced withthe transformer 300 of FIG. 3A. In some implementations (not shown), thetransformer 210 may be replaced with the transformer 350 of FIG. 3B. Insome implementations (not shown), a transformer winding may be swappedout to extend zero voltage switching in a wide input and/or outputvoltage range.

The system 200 includes an electrical load 250 connected between thefirst terminal 240 and the second terminal 242. For example, theelectrical load 250 may include a battery (e.g., a 12 volt battery or a48 volt battery).

The system 200 may include a rectifier, connecting the secondary winding212 of the transformer 210 to the electrical load 250. The rectifier maybe symmetric with respect to the first tap 214 and the second tap 216 ofthe secondary winding 212. The topology of the rectifier and/or asymmetric modulation scheme to control the switches (230, 232, and 234)of the rectifier may provide advantages over conventional half-bridgerectifiers. For example, the symmetric topology of the rectifier of thesystem 200 may enable reduction of unequal common-mode noise fromswitching. For example, the symmetric topology of the rectifier of thesystem 200 may enable the use components (e.g., capacitors or switches)with voltage ratings of half of the voltage level of the electrical load250. For example, the symmetric topology of the rectifier of the system200 may enable equal time derivative of the voltage signals at switchnodes. For example, the symmetric topology of the rectifier of thesystem 200 may enable full zero voltage switching operation for higherpower conversion efficiency.

The system 200 includes a first capacitor 220 connecting the first tap214 to a first node 244. The system 200 includes a second capacitor 222connecting the second tap 216 to a second node 246. The first capacitor220 and the second capacitor 222 may be direct current blocking seriescapacitors that can respectively have half of the voltage of rating of asingle direct current blocking series capacitor in a conventionalhalf-bridge rectifier. This may enable the use of smaller and/or lessexpensive capacitors, which may increase power density.

The system 200 includes a first switch 230 connecting the first node 244to a first terminal 240, a second switch 232 connecting the first node244 to the second node 246, and a third switch 234 connecting the secondnode 246 to a second terminal 242. For example, the first switch 230 maybe a field effect transistor (e.g., an n channel metal oxidesemiconductor field effect transistor) or another type of electronicswitch. For example, the second switch 232 may be a field effecttransistor (e.g., an n channel metal oxide semiconductor field effecttransistor) or another type of electronic switch. For example, the thirdswitch 234 may be a field effect transistor (e.g., an n channel metaloxide semiconductor field effect transistor) or another type ofelectronic switch. In some implementations, the control signals (e.g.,gate voltages) applied to the first switch 230, the second switch 232,and the third switch 234 are configured such that the first switch 230,the second switch 232, and the third switch 234 are not closed andconducting simultaneously to avoid shorting the electrical load 250 thatis connected between the first terminal 240 and the second terminal 242.

Control signals (e.g., gate voltages) for the switches (230, 232, and234) of the system 200 may be generated using a modulation scheme forsynchronous rectification of an AC voltage signal transferring powerthrough the transformer 210. Two-level voltage generation may be usedfor the AC voltage signal on the transformer 210. For example, amodulation scheme may be implemented to control the switches (230, 232,and 234) for two-level half-bridge rectification. The modulation schememay synchronously alternate between a first modulation state, in whichthe first switch 230 and the third switch 234 are closed (e.g.,conducting) and the second switch 232 is open (e.g., non-conducting)while the voltage on the transformer 210 is positive or high, and asecond modulation state, in which the first switch 230 and the thirdswitch 234 are open and the second switch 232 is closed while thevoltage on the transformer 210 is negative or low. Using these twosymmetric modulation states may serve to reduce common-mode noise andthus enable the use smaller electromagnetic interference filters or theomission of electromagnetic interference filters in some systems.

FIGS. 3A and 3B show two examples of transformers that can be used inpower converter systems described herein. FIG. 3A is a circuit diagramof an example of a transformer 300. The transformer 300 includes a firstprimary winding 310 and second primary winding 312 that are connected inseries between two taps of the transformer 300. The transformer 300includes a first secondary winding 320 and second secondary winding 322that are magnetically coupled respectively to the first primary winding310 and the second primary winding 312.

FIG. 3B is a circuit diagram of an example of a transformer 350. Thetransformer 350 includes a primary winding 360 that is magneticallycoupled to both a first secondary winding 370 and second secondarywinding 372. There may be design trade-offs between using thetransformer 300 versus the transformer 350 in a power converter system(e.g., the system 100 of FIG. 1A). For example, the transformer 300 maybe easier and less expensive to manufacture than the transformer 350.For example, the transformer 350 may be smaller than transformer 300 andmay enable greater power density in a power converter.

FIG. 4 is a circuit diagram of an example of a system 400 including ahybrid half bridge converter. The system 400 includes a transformer 410including a first secondary winding 411 and a second secondary winding412. The system 400 includes a rectifier, including a set of switches(430, 432, 434, 436, and 438), that connects taps of the first secondarywinding and the second secondary winding to a first terminal and asecond terminal. The rectifier may be symmetric with respect to thefirst secondary winding 411 and the second secondary winding 412. Thesystem 400 includes a first capacitor 420 connecting a first tap 414 ofthe first secondary winding 411 to a first node 444 of the rectifier;and a second capacitor 422 connecting a second tap (e.g., the third tap418) of the second secondary winding 412 to a second node 446 of therectifier. The system 400 includes an electrical load 450 connectedbetween the first terminal 440 and the second terminal 442. Theelectrical load 450 may include a battery (e.g., a 12 volt, a 48 volt, a400 volt, or an 800 volt battery) connected between the first terminal440 and the second terminal 442. The rectifier includes a capacitor 452in parallel with the electrical load 450. For example, the system 400may be implemented as part of the system 100 of FIG. 1A. For example,the system 400 may be implemented as part of the system 140 of FIG. 1B.For example, the system 400 may be implemented as part of the system 160of FIG. 1C.

In some implementations (not shown), the system 400 may include aprocessing apparatus (e.g., the processing apparatus 1010 of FIG. 10)that is configured to control the set of switches (430, 432, 434, 436,and 438) to rectify a multilevel voltage signal on the transformer 410.For example, the processing apparatus may be configured to select amodulation scheme from among two or more modulation schemes based on ameasured voltage level of the battery (of the electrical load 450). Forexample, a voltage sensor (e.g., a voltmeter) may be used to measure thevoltage level of the battery during operation of the system 400 todetermine the measured voltage level. In some implementations, a firstmodulation scheme of the two or more modulation schemes includesmodulation states that individually utilize one at a time of the firstsecondary winding 411 and the second secondary winding 412 to conductcurrent through the battery (of the electrical load 450), and a secondmodulation scheme of the two or more modulation schemes lacks modulationstates that individually utilize one at a time of the first secondarywinding 411 and the second secondary winding 412 to conduct currentthrough the battery. For example, the modulation scheme 500 of FIG. 5may be used when the measured battery voltage is near a high end of anoperating range of the battery (e.g., 60 volts) and the modulationscheme 600 of FIG. 6 may be used when the measured battery voltage isnear a low end of an operating range of the battery (e.g., 30 volts).

The system 400 includes a transformer 410 including a first secondarywinding 411, connecting a first tap 414 and a second tap 416, and asecond secondary winding 412, connecting a third tap 418 and the secondtap 416. For example, the transformer 410 may be the transformer 300 ofFIG. 3A. In some implementations (not shown), the transformer 410 may bereplaced with the transformer 350 of FIG. 3B. In some implementations(not shown), a transformer winding may be swapped out to extend zerovoltage switching in a wide input and/or output voltage range.

The system 400 includes an electrical load 450 connected between thefirst terminal 440 and the second terminal 442. For example, theelectrical load 450 may include a battery (e.g., a 12 volt battery or a48 volt battery).

The system 400 may include a rectifier, connecting the first secondarywinding 411 and the second secondary winding 412 of the transformer 410to the electrical load 450. The rectifier may be symmetric with respectto the first tap 414 and the third tap 418. The topology of therectifier and/or a symmetric modulation scheme to control the switches(430, 432, 434, 436 and 438) of the rectifier may provide advantagesover conventional half-bridge rectifiers. For example, the symmetrictopology of the rectifier of the system 400 may enable reduction ofunequal switching common-mode noise at transformer nodes. For example,the symmetric topology of the rectifier of the system 400 may enable theoption to swap-out a transformer winding to extend zero voltageswitching in a wide input and/or output voltage range. For example, thesymmetric topology of the rectifier of the system 400 may enable fulltransformer utilization (e.g., using both the first secondary winding411 and the second secondary winding 412 simultaneously) at higherbattery voltages, while enabling bypass of a transformer winding (e.g.,the first secondary winding 411 or the second secondary winding 412)under low battery voltage operation. For example, the symmetric topologyof the rectifier of the system 400 may enable full zero voltageswitching operation for higher power conversion efficiency.

The system 400 includes a first capacitor 420 connecting the first tap414 to a first node 444. The system 400 includes a second capacitor 422connecting the third tap 418 to a second node 446. The first capacitor420 and the second capacitor 422 may be direct current blocking seriescapacitors that can respectively have half of the voltage of rating of asingle direct current blocking series capacitor in a conventionalhalf-bridge rectifier. This may enable the use of smaller and/or lessexpensive capacitors, which may increase power density.

The system 400 includes a first switch 430 connecting the first node 444to a first terminal 440, a second switch 432 connecting the first node444 to the second node 446, and a third switch 434 connecting the secondnode 446 to a second terminal 442. For example, the first switch 430 maybe a field effect transistor (e.g., an n channel metal oxidesemiconductor field effect transistor) or another type of electronicswitch. For example, the second switch 432 may be a field effecttransistor (e.g., an n channel metal oxide semiconductor field effecttransistor) or another type of electronic switch. For example, the thirdswitch 434 may be a field effect transistor (e.g., an n channel metaloxide semiconductor field effect transistor) or another type ofelectronic switch. In some implementations, the control signals (e.g.,gate voltages) applied to the first switch 430, the second switch 432,and the third switch 434 are configured such that the first switch 430,the second switch 432, and the third switch 434 are not closed andconducting simultaneously to avoid shorting the electrical load 450 thatis connected between the first terminal 440 and the second terminal 442.

The system 400 includes a fourth switch 436 connecting the second tap416 to the first terminal 440, and a fifth switch 438 connecting thesecond tap 416 to the second terminal 442. For example, the fourthswitch 436 may be a field effect transistor (e.g., an n channel metaloxide semiconductor field effect transistor) or another type ofelectronic switch. For example, the fifth switch 438 may be a fieldeffect transistor (e.g., an n channel metal oxide semiconductor fieldeffect transistor) or another type of electronic switch. In someimplementations, the control signals (e.g., gate voltages) applied tothe fourth switch 436 and the fifth switch 438 are configured such thatthe fourth switch 436 and the fifth switch 438 are not closed andconducting simultaneously to avoid shorting the electrical load 450 thatis connected between the first terminal 440 and the second terminal 442.

FIG. 5 is a plot of an example of a modulation scheme 500 for switchesof a hybrid half bridge converter with corresponding transformer voltageand current signals. For example, the modulation scheme 500 may be usedwith the system 400 when a battery of the electrical load 450 ismeasured to have a voltage level (e.g., 60 volts) near an upper end ofan operating range for the battery. The modulation scheme 500 may beused to control the switches (430, 432, 434, 436, and 438) of the system400 to rectify voltage on the transformer 410. The plot of themodulation scheme 500 includes a plot of a voltage signal 510 across aprimary winding of the transformer 410; a plot of a current signal 512through a primary winding of the transformer 410; a plot of Su1R 514,which is a control signal (e.g., a gate voltage) that controls theswitch 430; a plot of Su1 v 1 516, which is a control signal (e.g., agate voltage) that controls the switch 432; a plot of Sv1S 518, which isa control signal (e.g., a gate voltage) that controls the switch 434; aplot of Su2R 520, which is a control signal (e.g., a gate voltage) thatcontrols the switch 436; and a plot of Sv2S 522, which is a controlsignal (e.g., a gate voltage) that controls the switch 438. The plot isdivided horizontally into time intervals (530-540) corresponding tomodulation states of the modulation scheme 500. The modulation scheme500 may be implemented by a system including a processing apparatus(e.g., the system 1000, including the processing apparatus 1010, of FIG.10) and the system 400. The processing apparatus may be configured tocontrol the first switch 430, the second switch 432, the third switch434, the fourth switch 436, and the fifth switch 438 to rectify themultilevel voltage signal 510 on the transformer 410. For example, thevoltage signal 510 and the current signal 512 may be generated based inpart on control of synchronous switching in an inverter (e.g., theinverter 120 or the inverter 1042) connected to taps of the primarywinding of the transformer 410.

The plot of the modulation scheme 500 covers two periods (t=0 to t=T_sand t=T_s to t=2*T_s) of the voltage signal 510 on the transformer.During the time interval 530 (starting at time t=0) the modulationscheme 500 is in a state labeled “C1” where the voltage signal 510 isnegative and the control signals Su1R 514, Su1 v 1 516, and Su2R 520 arehigh and the control signals Sv1S 518 and Sv2S 522 are low,corresponding to switch 430, switch 432, and switch 436 being in aclosed (e.g., conducting) state and to switch 434 and switch 438 beingin a an open (e.g., non-conducting) state. During the time interval 532the state of the modulation scheme 500 is labeled “A” where the voltagesignal 510 is positive and the control signals Su1R 514 and Sv1S 518 arehigh and the control signals Su1 v 1 516, Su2R 520, and Sv2S 522 arelow, corresponding to switch 432, switch 436, and switch 438 being in anopen state and to switch 430 and switch 434 being in a closed state.During the time interval 534 the state of the modulation scheme 500 islabeled “C2” where the voltage signal 510 is negative and the controlsignals Su1 v 1 516, Sv1S 518, and Sv2S 522 are high and the controlsignals Su1R 514 and Su2R 520 are low, corresponding to switch 432,switch 434, and switch 438 being in a closed state and to switch 430 andswitch 436 being in an open state. During the time interval 536 thestate of the modulation scheme 500 is labeled “C2” where the voltagesignal 510 is negative and the control signals Su1 v 1 516, Sv1S 518,and Sv2S 522 are high and the control signals Su1R 514 and Su2R 520 arelow, corresponding to switch 432, switch 434, and switch 438 being in aclosed state and to switch 430 and switch 436 being in an open state.During the time interval 538 the state of the modulation scheme 500 islabeled “A” where the voltage signal 510 is positive and the controlsignals Su1R 514 and Sv1S 518 are high and the control signals Su1 v 1516, Su2R 520, and Sv2S 522 are low, corresponding to switch 432, switch436, and switch 438 being in an open state and to switch 430 and switch434 being in a closed state. During the time interval 540 the state ofthe modulation scheme 500 is labeled “C1” where the voltage signal 510is negative and the control signals Su1R 514, Su1 v 1 516, and Su2R 520are high and the control signals Sv1S 518 and Sv2S 522 are low,corresponding to switch 430, switch 432, and switch 436 being in aclosed state and to switch 434 and switch 438 being in a an open state.

For example, the modulation scheme 500 includes: in a first state (e.g.,labeled “C1”) corresponding to a first voltage level (e.g., a negativevoltage level), opening the third switch 434 and the fifth switch 438and closing the first switch 430, the second switch 432, and the fourthswitch 436; and in a second state (e.g., labeled “C2”) corresponding tothe first voltage level, opening the first switch 430 and the fourthswitch 436 and closing the second switch 432, the third switch 434, andthe fifth switch 438. In some implementations, a processing apparatus(e.g. the processing apparatus 1010 of FIG. 10) is configured to changea phase of the first state and the second state between periods of themultilevel voltage signal 510 on the transformer 410.

The modulation scheme 500 may provide some advantages. For example, themodulation scheme 500 may be used with the system 400 when a battery ofthe electrical load 450 is measured to have a voltage level (e.g., 60volts) near an upper end of an operating range for the battery, as partof supporting a wide input and/or output voltage level. The modulationscheme 500 may enable full elimination of unequal switching common-modenoise at the transformer 410 nodes. For example, the modulation scheme500 may enable full transformer utilization (e.g., using both the firstsecondary winding 411 and the second secondary winding 412simultaneously) at higher battery voltages. Both transformer windings(411 and 412) are utilized to get full voltage usage of battery andtransformers. For example, the first secondary winding 411 and thesecond secondary winding 412 may respectively see half the batteryvoltage. For example, the modulation scheme 500 may enable full zerovoltage switching operation for higher power conversion efficiency.

FIG. 6 is a plot of an example of a modulation scheme 600 for switchesof a hybrid half bridge converter with corresponding transformer voltageand current signals. For example, the modulation scheme 600 may be usedwith the system 400 when a battery of the electrical load 450 ismeasured to have a voltage level (e.g., 30 volts) near a lower end of anoperating range for the battery. The modulation scheme 600 may be usedto control the switches (430, 432, 434, 436, and 438) of the system 400to rectify voltage on the transformer 410. The plot of the modulationscheme 600 includes a plot of a voltage signal 610 across a primarywinding of the transformer 410; a plot of a current signal 612 through aprimary winding of the transformer 410; a plot of Su1R 614, which is acontrol signal (e.g., a gate voltage) that controls the switch 430; aplot of Su1 v 1 616, which is a control signal (e.g., a gate voltage)that controls the switch 432; a plot of Sv1S 618, which is a controlsignal (e.g., a gate voltage) that controls the switch 434; a plot ofSu2R 620, which is a control signal (e.g., a gate voltage) that controlsthe switch 436; and a plot of Sv2S 622, which is a control signal (e.g.,a gate voltage) that controls the switch 438. The plot is dividedhorizontally into time intervals (630-640) corresponding to modulationstates of the modulation scheme 600. The modulation scheme 600 may beimplemented by a system including a processing apparatus (e.g., thesystem 1000, including the processing apparatus 1010, of FIG. 10) andthe system 400. The processing apparatus may be configured to controlthe first switch 430, the second switch 432, the third switch 434, thefourth switch 436, and the fifth switch 438 to rectify the multilevelvoltage signal 610 on the transformer 410. For example, the voltagesignal 610 and the current signal 612 may be generated based in part oncontrol of synchronous switching in an inverter (e.g., the inverter 120or the inverter 1042) connected to taps of the primary winding of thetransformer 410.

The plot of the modulation scheme 600 covers two periods (t=0 to t=T_sand t=T_s to t=2*T_s) of the voltage signal 610 on the transformer.During the time interval 630 (starting at time t=0) the modulationscheme 600 is in a state labeled “C1” where the voltage signal 610 isnegative and the control signals Su1R 614, Su1 v 1 616, and Su2R 620 arehigh and the control signals Sv1S 618 and Sv2S 622 are low,corresponding to switch 430, switch 432, and switch 436 being in aclosed (e.g., conducting) state and to switch 434 and switch 438 beingin a an open (e.g., non-conducting) state. During the time interval 632the state of the modulation scheme 600 is labeled “D” where the voltagesignal 610 is positive and the control signals Su1R 614, Sv1S 618, andSv2S 622 are high and the control signals Su1 v 1 616 and Su2R 620 arelow, corresponding to switch 432 and switch 436 being in an open stateand to switch 430, switch 434, and switch 438 being in a closed state.During the time interval 634 the state of the modulation scheme 600 islabeled “C2” where the voltage signal 610 is negative and the controlsignals Su1 v 1 616, Sv1S 618, and Sv2S 622 are high and the controlsignals Su1R 614 and Su2R 620 are low, corresponding to switch 432,switch 434, and switch 438 being in a closed state and to switch 430 andswitch 436 being in an open state. During the time interval 636 thestate of the modulation scheme 600 is labeled “C2” where the voltagesignal 610 is negative and the control signals Su1 v 1 616, Sv1S 618,and Sv2S 622 are high and the control signals Su1R 614 and Su2R 620 arelow, corresponding to switch 432, switch 434, and switch 438 being in aclosed state and to switch 430 and switch 436 being in an open state.During the time interval 638 the state of the modulation scheme 600 islabeled “B” where the voltage signal 610 is positive and the controlsignals Su1R 614, Sv1S 618, and Su2R 620 are high and the controlsignals Su1 v 1 616 and Sv2S 622 are low, corresponding to switch 432and switch 438 being in an open state and to switch 430, switch 434, andswitch 436 being in a closed state. During the time interval 640 thestate of the modulation scheme 600 is labeled “C1” where the voltagesignal 610 is negative and the control signals Su1R 614, Su1 v 1 616,and Su2R 620 are high and the control signals Sv1S 618 and Sv2S 622 arelow, corresponding to switch 430, switch 432, and switch 436 being in aclosed state and to switch 434 and switch 438 being in a an open state.

For example, the modulation scheme 600 includes: in a first state (e.g.,labeled “C1”) corresponding to a first voltage level (e.g., a negativevoltage level), opening the third switch 434 and the fifth switch 438and closing the first switch 430, the second switch 432, and the fourthswitch 436; and in a second state (e.g., labeled “C2”) corresponding tothe first voltage level, opening the first switch 430 and the fourthswitch 436 and closing the second switch 432, the third switch 434, andthe fifth switch 438. In some implementations, a processing apparatus(e.g. the processing apparatus 1010 of FIG. 10) is configured to changea phase of the first state and the second state between periods of themultilevel voltage signal 610 on the transformer 410. For example, themodulation scheme 600 includes: in a third state (e.g., labeled “B”)corresponding to a second voltage level (e.g., a positive voltagelevel), opening the second switch 432 and the fifth switch 438 andclosing the first switch 430, the third switch 434, and the fourthswitch 434; and in a fourth state (e.g., labeled “D”) corresponding tothe second voltage level, opening the second switch 432 and the fourthswitch 436 and closing the first switch 430, the third switch 434, andthe fifth switch 438.

The modulation scheme 600 may provide some advantages. For example, themodulation scheme 600 may be used with the system 400 when a battery ofthe electrical load 450 is measured to have a voltage level (e.g., 30volts) near a lower end of an operating range for the battery, as partof supporting a wide input and/or output voltage level. The modulationscheme 600 may enable reduction of unequal switching common-mode noiseat transformer 410 nodes. For example, the modulation scheme 600 mayenable full zero voltage switching operation for higher power conversionefficiency. For example, the modulation scheme 600 may swap-out one ofthe two transformer windings to utilize the low battery voltagecondition and still push high current to facilitate zero voltageswitching. For example, the first secondary winding 411 may beswapped-out during the modulation state labeled “B” (e.g., as shown inthe time interval 638). For example, the second secondary winding 412may be swapped-out during the modulation state labeled “D” (e.g., asshown in the time interval 632). Each secondary winding of thetransformer 410 may be swapped-out in every other cycle to help balancecurrent among windings.

FIG. 7 is circuit diagram of an example of a system 700 including ahybrid full bridge converter. The system 700 includes a transformer 710including a first secondary winding 711 and a second secondary winding712. The system 700 includes a rectifier, including a set of switches(730, 732, 734, 736, 737, and 738), that connects taps of the firstsecondary winding and the second secondary winding to a first terminaland a second terminal. The rectifier may be symmetric with respect tothe first secondary winding 711 and the second secondary winding 712.The system 700 includes an electrical load 750 connected between thefirst terminal 740 and the second terminal 742. The electrical load 750may include a battery (e.g., a 12 volt, a 48 volt, a 400 volt, or an 800volt battery) connected between the first terminal 740 and the secondterminal 742. The rectifier includes a capacitor 752 in parallel withthe electrical load 750. For example, the system 700 may be implementedas part of the system 100 of FIG. 1A. For example, the system 700 may beimplemented as part of the system 140 of FIG. 1B. For example, thesystem 700 may be implemented as part of the system 160 of FIG. 1C.

In some implementations (not shown), the system 700 may include aprocessing apparatus (e.g., the processing apparatus 1010 of FIG. 10)that is configured to control the set of switches (730, 732, 734, 736,737, and 738) to rectify a multilevel voltage signal on the transformer710. For example, the processing apparatus may be configured to select amodulation scheme from among two or more modulation schemes based on ameasured voltage level of the battery (of the electrical load 750). Forexample, a voltage sensor (e.g., a voltmeter) may be used to measure thevoltage level of the battery during operation of the system 700 todetermine the measured voltage level. In some implementations, a firstmodulation scheme of the two or more modulation schemes includesmodulation states that individually utilize one at a time of the firstsecondary winding 711 and the second secondary winding 712 to conductcurrent through the battery (of the electrical load 750), and a secondmodulation scheme of the two or more modulation schemes lacks modulationstates that individually utilize one at a time of the first secondarywinding 711 and the second secondary winding 712 to conduct currentthrough the battery. For example, the modulation scheme 800 of FIG. 8may be used when the measured battery voltage is near a high end of anoperating range of the battery (e.g., 60 volts) and the modulationscheme 900 of FIG. 9 may be used when the measured battery voltage isnear a low end of an operating range of the battery (e.g., 30 volts).

The system 700 includes a transformer 710 including a first secondarywinding 711, connecting a first tap 714 and a second tap 716, and asecond secondary winding 712, connecting a third tap 718 and a fourthtap 720. For example, the transformer 710 may be the transformer 300 ofFIG. 3A. In some implementations (not shown), the transformer 710 may bereplaced with the transformer 350 of FIG. 3B. In some implementations(not shown), a transformer winding may be swapped out to extend zerovoltage switching in a wide input and/or output voltage range.

The system 700 includes an electrical load 750 connected between thefirst terminal 740 and the second terminal 742. For example, theelectrical load 750 may include a battery (e.g., a 12 volt battery or a48 volt battery).

The system 700 includes a first switch 730 connecting the first tap 714to a first terminal 740, a second switch 732 connecting the first tap714 to the fourth tap 720, and a third switch 734 connecting the fourthtap 720 to a second terminal 742. For example, the first switch 730 maybe a field effect transistor (e.g., an n channel metal oxidesemiconductor field effect transistor) or another type of electronicswitch. For example, the second switch 732 may be a field effecttransistor (e.g., an n channel metal oxide semiconductor field effecttransistor) or another type of electronic switch. For example, the thirdswitch 734 may be a field effect transistor (e.g., an n channel metaloxide semiconductor field effect transistor) or another type ofelectronic switch. In some implementations, the control signals (e.g.,gate voltages) applied to the first switch 730, the second switch 732,and the third switch 734 are configured such that the first switch 730,the second switch 732, and the third switch 734 are not closed andconducting simultaneously to avoid shorting the electrical load 750 thatis connected between the first terminal 740 and the second terminal 742.

The system 700 includes a fourth switch 736 connecting the second tap716 to the first terminal 740, a fifth switch 737 connecting the secondtap 716 to the third tap 718, and a sixth switch 738 connecting thethird tap 718 to the second terminal 742. For example, the fourth switch736 may be a field effect transistor (e.g., an n channel metal oxidesemiconductor field effect transistor) or another type of electronicswitch. For example, the fifth switch 737 may be a field effecttransistor (e.g., an n channel metal oxide semiconductor field effecttransistor) or another type of electronic switch. For example, the sixthswitch 738 may be a field effect transistor (e.g., an n channel metaloxide semiconductor field effect transistor) or another type ofelectronic switch. In some implementations, the control signals (e.g.,gate voltages) applied to the fourth switch 736, the fifth switch 737,and the sixth switch 738 are configured such that the fourth switch 736,the fifth switch 737, and the sixth switch 738 are not closed andconducting simultaneously to avoid shorting the electrical load 750 thatis connected between the first terminal 740 and the second terminal 742.

The system 700 may include a rectifier, connecting the first secondarywinding 711 and the second secondary winding 712 of the transformer 710to the electrical load 750. The rectifier may be symmetric with respectto the first tap 714 and the fourth tap 720. The topology of therectifier and/or a symmetric modulation scheme to control the switches(730, 732, 734, 736, 737, and 738) of the rectifier may provideadvantages over conventional full-bridge rectifiers. For example, thesymmetric topology of the rectifier of the system 700 may enablereduction of unequal switching common-mode noise at transformer nodes.For example, the symmetric topology of the rectifier of the system 700may enable full zero voltage switching operation for higher powerconversion efficiency. For example, the symmetric topology of therectifier of the system 700 may enable the option to swap-out atransformer winding to extend zero voltage switching in a wide inputand/or output voltage range. For example, the symmetric topology of therectifier of the system 700 may enable full transformer utilization(e.g., using both the first secondary winding 711 and the secondsecondary winding 712 simultaneously) at higher battery voltages, whileenabling bypass of a transformer winding (e.g., the first secondarywinding 711 or the second secondary winding 712) under low batteryvoltage operation. For example, the symmetric topology of the rectifierof the system 700 may support bipolar full-bridge voltage operation,which may enable the omission of blocking capacitors in the system 700.

Control signals (e.g., gate voltages) for the switches (730, 732, 734,736, 737, and 738) of the system 700 may be generated using a modulationscheme for synchronous rectification of an AC voltage signaltransferring power through the transformer 710. Multilevel voltagegeneration (e.g., three-level or five-level) may be used for the ACvoltage signal on the transformer 710. Using a multilevel voltage signalon the transformer 710 may offer advantages, such as lowering the timederivative if the voltage across the transformer 710, which may reducecore losses in the transformer 710. Using a multilevel voltage signal onthe transformer 710 may cause the current through the windings of thetransformer 710 to more closely approximate sinusoidal currents, whichmay reduce copper losses. Using a multilevel voltage signal on thetransformer 710 may enable greater control flexibility to cover widerinput and/or output voltage fluctuations. For example, the modulationscheme 800 of FIG. 8 may be implemented to control the switches (730,732, 734, 736, 737, and 738). For example, the modulation scheme 900 ofFIG. 9 may be implemented to control the switches (730, 732, 734, 736,737, and 738).

FIG. 8 is a plot of an example of a modulation scheme 800 for switchesof a hybrid full bridge converter with corresponding transformer voltageand current signals. For example, the modulation scheme 800 may be usedwith the system 700 when a battery of the electrical load 750 ismeasured to have a voltage level (e.g., 60 volts) near an upper end ofan operating range for the battery. The modulation scheme 800 may beused to control the switches (730, 732, 734, 736, 737, and 738) of thesystem 700 to rectify voltage on the transformer 710. The plot of themodulation scheme 800 includes a plot of a voltage signal 810 across aprimary winding of the transformer 710; a plot of a current signal 812through a primary winding of the transformer 710; a plot of Su1R 814,which is a control signal (e.g., a gate voltage) that controls theswitch 730; a plot of Su1 v 1 816, which is a control signal (e.g., agate voltage) that controls the switch 732; a plot of Sv1S 818, which isa control signal (e.g., a gate voltage) that controls the switch 734; aplot of Su2R 820, which is a control signal (e.g., a gate voltage) thatcontrols the switch 736; a plot of Su2 v 2 822, which is a controlsignal (e.g., a gate voltage) that controls the switch 737; and a plotof Sv2S 824, which is a control signal (e.g., a gate voltage) thatcontrols the switch 738. The plot is divided horizontally into timeintervals (830-844) corresponding to modulation states of the modulationscheme 800. The modulation scheme 800 may be implemented by a systemincluding a processing apparatus (e.g., the system 1000, including theprocessing apparatus 1010, of FIG. 10) and the system 700. Theprocessing apparatus may be configured to control the first switch 730,the second switch 732, the third switch 734, the fourth switch 736, thefifth switch 737, and the sixth switch 738 to rectify the multilevelvoltage signal 810 on the transformer 710. For example, the voltagesignal 810 and the current signal 812 may be generated based in part oncontrol of synchronous switching in an inverter (e.g., the inverter 120or the inverter 1042) connected to taps of the primary winding of thetransformer 710.

The plot of the modulation scheme 800 covers two periods (t=0 to t=T_sand t=T_s to t=2*T_s) of the voltage signal 810 on the transformer.During the time interval 830 (starting at time t=0) the modulationscheme 800 is in a state labeled “C1” where the voltage signal 810 iszero and the control signals Su1R 814, Sv1S 818, Su2R 820, and Sv2S 824are high and the control signals Su1 v 1 816 and Su2 v 2 822 are low,corresponding to switch 730, switch 734, switch 736, and switch 738being in a closed (e.g., conducting) state and to switch 732 and switch737 being in an open (e.g., non-conducting) state. During the timeinterval 832 the state of the modulation scheme 800 is labeled “A” wherethe voltage signal 810 is positive and the control signals Su1R 814,Sv1S 818, and Su2 v 2 822 are high and the control signals Su1 v 1 816,Su2R 820, and Sv2S 824 are low, corresponding to switch 732, switch 736,and switch 738 being in an open state and to switch 730, switch 734, andswitch 737 being in a closed state. During the time interval 834 thestate of the modulation scheme 800 is labeled “C1” where the voltagesignal 810 is zero and the control signals Su1R 814, Sv1S 818, Su2R 820,and Sv2S 824 are high and the control signals Su1 v 1 816 and Su2 v 2822 are low, corresponding to switch 730, switch 734, switch 736, andswitch 738 being in a closed state and to switch 732 and switch 737being in an open state. During the time interval 836 the state of themodulation scheme 800 is labeled “B” where the voltage signal 810 isnegative and the control signals Su1 v 1 816, Su2R 820, and Sv2S 824 arehigh and the control signals Su1R 814, Sv1S 818, and Su2 v 2 822 arelow, corresponding to switch 732, switch 736, and switch 738 being in aclosed state and to switch 730, switch 734, and switch 737 being in anopen state. During the time interval 838 the state of the modulationscheme 800 is labeled “C1” where the voltage signal 810 is zero and thecontrol signals Su1R 814, Sv1S 818, Su2R 820, and Sv2S 824 are high andthe control signals Su1 v 1 816 and Su2 v 2 822 are low, correspondingto switch 730, switch 734, switch 736, and switch 738 being in a closedstate and to switch 732 and switch 737 being in an open state. Duringthe time interval 840 the state of the modulation scheme 800 is labeled“A” where the voltage signal 810 is positive and the control signalsSu1R 814, Sv1S 818, and Su2 v 2 822 are high and the control signals Su1v 1 816, Su2R 820, and Sv2S 824 are low, corresponding to switch 732,switch 736, and switch 738 being in an open state and to switch 730,switch 734, and switch 737 being in a closed state. During the timeinterval 842 the state of the modulation scheme 800 is labeled “C1”where the voltage signal 810 is zero and the control signals Su1R 814,Sv1S 818, Su2R 820, and Sv2S 824 are high and the control signals Su1 v1 816 and Su2 v 2 822 are low, corresponding to switch 730, switch 734,switch 736, and switch 738 being in a closed state and to switch 732 andswitch 737 being in an open state. During the time interval 844 thestate of the modulation scheme 800 is labeled “B” where the voltagesignal 810 is negative and the control signals Su1 v 1 816, Su2R 820,and Sv2S 824 are high and the control signals Su1R 814, Sv1S 818, andSu2 v 2 822 are low, corresponding to switch 732, switch 736, and switch738 being in a closed state and to switch 730, switch 734, and switch737 being in an open state.

The modulation scheme 800 may provide some advantages. For example, themodulation scheme 800 may be used with the system 700 when a battery ofthe electrical load 750 is measured to have a voltage level (e.g., 60volts) near an upper end of an operating range for the battery, as partof supporting a wide input and/or output voltage level. The modulationscheme 800 may enable full elimination of unequal switching common-modenoise at the transformer 710 nodes. For example, the modulation scheme800 may enable full zero voltage switching operation for higher powerconversion efficiency. For example, the modulation scheme 800 may enablefull transformer utilization (e.g., using both the first secondarywinding 711 and the second secondary winding 712 simultaneously) athigher battery voltages. Both transformer windings (711 and 712) areutilized to get full voltage usage of battery and transformers. Forexample, the first secondary winding 711 and the second secondarywinding 712 may respectively see half the battery voltage.

FIG. 9 is a plot of an example of a modulation scheme 900 for switchesof a hybrid full bridge converter with corresponding transformer voltageand current signals. For example, the modulation scheme 900 may be usedwith the system 700 when a battery of the electrical load 750 ismeasured to have a voltage level (e.g., 30 volts) near a lower end of anoperating range for the battery. The modulation scheme 900 may be usedto control the switches (730, 732, 734, 736, 737, and 738) of the system700 to rectify voltage on the transformer 710. The plot of themodulation scheme 900 includes a plot of a voltage signal 910 across aprimary winding of the transformer 710; a plot of a current signal 912through a primary winding of the transformer 710; a plot of Su1R 914,which is a control signal (e.g., a gate voltage) that controls theswitch 730; a plot of Su1 v 1 916, which is a control signal (e.g., agate voltage) that controls the switch 732; a plot of Sv1S 918, which isa control signal (e.g., a gate voltage) that controls the switch 734; aplot of Su2R 920, which is a control signal (e.g., a gate voltage) thatcontrols the switch 736; a plot of Su2 v 2 922, which is a controlsignal (e.g., a gate voltage) that controls the switch 737; and a plotof Sv2S 924, which is a control signal (e.g., a gate voltage) thatcontrols the switch 738. The plot is divided horizontally into timeintervals (930-944) corresponding to modulation states of the modulationscheme 900. The modulation scheme 900 may be implemented by a systemincluding a processing apparatus (e.g., the system 1000, including theprocessing apparatus 1010, of FIG. 10) and the system 700. Theprocessing apparatus may be configured to control the first switch 730,the second switch 732, the third switch 734, the fourth switch 736, thefifth switch 737, and the sixth switch 738 to rectify the multilevelvoltage signal 910 on the transformer 710. For example, the voltagesignal 910 and the current signal 912 may be generated based in part oncontrol of synchronous switching in an inverter (e.g., the inverter 120or the inverter 1042) connected to taps of the primary winding of thetransformer 710.

The plot of the modulation scheme 900 covers two periods (t=0 to t=T_sand t=T_s to t=2*T_s) of the voltage signal 910 on the transformer 710.During the time interval 930 (starting at time t=0) the modulationscheme 900 is in a state labeled “C1” where the voltage signal 910 iszero and the control signals Su1R 914, Sv1S 918, Su2R 920, and Sv2S 924are high and the control signals Su1 v 1 916 and Su2 v 2 922 are low,corresponding to switch 730, switch 734, switch 736, and switch 738being in a closed (e.g., conducting) state and to switch 732 and switch737 being in an open (e.g., non-conducting) state. During the timeinterval 932 the state of the modulation scheme 900 is labeled “D1”where the voltage signal 910 is positive and the control signals Su1R914, Sv1S 918, Su2R 920, and Su2 v 2 922 are high and the controlsignals Su1 v 1 916 and Sv2S 924 are low, corresponding to switch 732and switch 738 being in an open state and to switch 730, switch 734,switch 736, and switch 737 being in a closed state. During the timeinterval 934 the state of the modulation scheme 900 is labeled “C1”where the voltage signal 910 is zero and the control signals Su1R 914,Sv1S 918, Su2R 920, and Sv2S 924 are high and the control signals Su1 v1 916 and Su2 v 2 922 are low, corresponding to switch 730, switch 734,switch 736, and switch 738 being in a closed state and to switch 732 andswitch 737 being in an open state. During the time interval 936 thestate of the modulation scheme 900 is labeled “E1” where the voltagesignal 910 is negative and the control signals Su1 v 1 916, Sv1S 918,Su2R 920, and Sv2S 924 are high and the control signals Su1R 914 and Su2v 2 922 are low, corresponding to switch 732, switch 734, switch 736,and switch 738 being in a closed state and to switch 730 and switch 737being in an open state. During the time interval 938 the state of themodulation scheme 900 is labeled “C1” where the voltage signal 910 iszero and the control signals Su1R 914, Sv1S 918, Su2R 920, and Sv2S 924are high and the control signals Su1 v 1 916 and Su2 v 2 922 are low,corresponding to switch 730, switch 734, switch 736, and switch 738being in a closed state and to switch 732 and switch 737 being in anopen state. During the time interval 940 the state of the modulationscheme 900 is labeled “D2” where the voltage signal 910 is positive andthe control signals Su1R 914, Sv1S 918, Su2 v 2 922, and Sv2S 924 arehigh and the control signals Su1 v 1 916, Su2R 920, are low,corresponding to switch 732 and switch 736 being in an open state and toswitch 730, switch 734, switch 737, and switch 738 being in a closedstate. During the time interval 942 the state of the modulation scheme900 is labeled “C1” where the voltage signal 910 is zero and the controlsignals Su1R 914, Sv1S 918, Su2R 920, and Sv2S 924 are high and thecontrol signals Su1 v 1 916 and Su2 v 2 922 are low, corresponding toswitch 730, switch 734, switch 736, and switch 738 being in a closedstate and to switch 732 and switch 737 being in an open state. Duringthe time interval 944 the state of the modulation scheme 900 is labeled“E2” where the voltage signal 910 is negative and the control signalsSu1R 914, Su1 v 1 916, Su2R 920, and Sv2S 924 are high and the controlsignals Sv1S 918, and Su2 v 2 922 are low, corresponding to switch 730,switch 732, switch 736, and switch 738 being in a closed state and toswitch 734, and switch 737 being in an open state.

For example, the modulation scheme 900 includes: in a first state (e.g.,labeled “D1”) corresponding to a first voltage level (e.g., a positivevoltage level), opening the second switch 732 and the sixth switch 738and closing the first switch 730, the third switch 734, the fourthswitch 736, and the fifth switch 737; and in a second state (e.g.,labeled “D2”) corresponding to the first voltage level, opening thesecond switch 732 and the fourth switch 736 and closing the first switch730, the third switch 734, the fifth switch 737, and the sixth switch738. For example, the modulation scheme 900 includes: in a third state(e.g., labeled “E1”) corresponding to a second voltage level (e.g., anegative voltage level), opening the first switch 730 and the fifthswitch 737 and closing the second switch 732, the third switch 734, thefourth switch 736, and the sixth switch 738; and in a fourth state(e.g., labeled “E2”) corresponding to the second voltage level, openingthe third switch 734 and the fifth switch 737 and closing the firstswitch 730, the second switch 732, the fourth switch 736, and the sixthswitch 738.

The modulation scheme 900 may provide some advantages. For example, themodulation scheme 900 may be used with the system 700 when a battery ofthe electrical load 750 is measured to have a voltage level (e.g., 30volts) near a lower end of an operating range for the battery, as partof supporting a wide input and/or output voltage level. The modulationscheme 900 may enable reduction of unequal switching common-mode noiseat transformer 710 nodes. For example, the modulation scheme 900 mayenable full zero voltage switching operation for higher power conversionefficiency. For example, the modulation scheme 900 may swap-out one ofthe two transformer windings to utilize the low battery voltagecondition and still push high current to facilitate zero voltageswitching. For example, the first secondary winding 711 may beswapped-out during the modulation state labeled “D1” (e.g., as shown inthe time interval 932). For example, the second secondary winding 712may be swapped-out during the modulation state labeled “D2” (e.g., asshown in the time interval 940). Each secondary winding of thetransformer 710 may be swapped-out in every other cycle to help balancecurrent among windings.

FIG. 10 is a block diagram of an example of a system 1000 for powerconversion. The system 1000 may include a processing apparatus 1010, adata storage device 1020, a sensor interface 1030, a pulse widthmodulation interface 1040 to an inverter 1042 and a rectifier 1044, andan interconnect 1050 through which the processing apparatus 1010 mayaccess the other components. The system 1000 may be configured tocontrol a power converter (e.g., a DC/DC converter) including theinverter 1042 and/or the rectifier 1044. For example, the rectifier 1044may include the rectifier of system 200 of FIG. 2. For example, therectifier 1044 may include the rectifier of system 400 of FIG. 4. Forexample, the rectifier 1044 may include the rectifier of system 700 ofFIG. 7.

The processing apparatus 1010 is operable to execute instructions thathave been stored in a data storage device 1020. In some implementations,the processing apparatus 1010 is a processor with random access memoryfor temporarily storing instructions read from the data storage device1020 while the instructions are being executed. The processing apparatus1010 may include single or multiple processors each having single ormultiple processing cores. Alternatively, the processing apparatus 1010may include another type of device, or multiple devices, capable ofmanipulating or processing data. For example, the data storage device1020 may be a non-volatile information storage device such as a harddrive, a solid-state drive, a read-only memory device (ROM), an opticaldisc, a magnetic disc, or any other suitable type of storage device suchas a non-transitory computer readable memory. The data storage device1020 may include another type of device, or multiple devices, capable ofstoring data for retrieval or processing by the processing apparatus1010. For example, the data storage device 1020 can be distributedacross multiple machines or devices such as network-based memory ormemory in multiple machines performing operations that can be describedherein as being performed using a single computing device for ease ofexplanation. The processing apparatus 1010 may access and manipulatedata in stored in the data storage device 1020 via interconnect 1050.For example, the data storage device 1020 may store instructionsexecutable by the processing apparatus 1010 that upon execution by theprocessing apparatus 1010 cause the processing apparatus 1010 to performoperations (e.g., operations that implement the modulation scheme 500 ofFIG. 5, the modulation scheme 600 of FIG. 6, the modulation scheme 800of FIG. 8, and/or the modulation scheme 900 of FIG. 9).

The sensor interface 1030 may be configured to control and/or receivedata (e.g., voltage and/or current measurements for one or more windingsof a transformer that magnetically couples the inverter 1042 to therectifier 1044) from one or more sensors (e.g., a voltmeter or anammeter). In some implementations, the sensor interface 1030 mayimplement a serial port protocol (e.g., I2C or SPI) for communicationswith one or more sensor devices over conductors. In someimplementations, the sensor interface 1030 may include a wirelessinterface for communicating with one or more sensor groups vialow-power, short-range communications (e.g., using a local area networkprotocol).

The pulse width modulation interface 1040 allows input and output ofinformation to other systems to facilitate automated control of thosesystems. For example, the pulse width modulation interface 1040 mayinclude latches, crystal oscillators, clocking circuits, and other logiccircuits for generating control signals for switches in the inverter1042 and the rectifier 1044. For example, the control signals may bebinary pulse width modulated voltage signals. The pulse width modulationinterface 1040 may generate control signals for switches in the inverter1042 and the rectifier 1044 in response to one or more commands from theprocessing apparatus 1010. For example, the interconnect 1050 may be asystem bus, or a wired or wireless network.

For example, the processing apparatus 1010 and/or the pulse widthmodulation interface 1040 may implement a pulse width modulationcontroller for a DC/DC power converter (e.g., the system 100 of FIG. 1A)including the inverter 1042 magnetically coupled to the rectifier 1044via a transformer (e.g., the transformer 300 of FIG. 3A or thetransformer 350 of FIG. 3B). The pulse width modulation controller mayimplement a modulation scheme (e.g., the modulation scheme 500 of FIG.5, the modulation scheme 600 of FIG. 6, the modulation scheme 800 ofFIG. 8, and/or the modulation scheme 900 of FIG. 9) and dynamicallyadjust control parameters of the modulation scheme. For example, thecontrol parameters of the modulation scheme may include a duty cycle ofthe inverter 1042, a duty cycle of the rectifier 1044, a phase betweencontrol signaling for the inverter 1042 and control signaling for therectifier 1044, and/or the switching frequency for the DC/DC powerconverter. The control parameters of the pulse width modulationcontroller may be adjusted based on operating parameters of the DC/DCpower converter that are sensed (e.g., using sensors accessed via thesensor interface 1030). For example, the operating parameters mayinclude an input DC voltage (e.g., voltage of the high voltage battery102), an output DC voltage (e.g., voltage of the low voltage battery104), and/or a current in DC/DC power converter (e.g., a current througha primary winding or a secondary winding of the transformer). Forexample, the pulse width modulation controller may implement amodulation scheme with zero voltage switching or zero current switching.

FIG. 11 is a flow chart of an example of a process 1100 for controllingswitches of a rectifier for power conversion. The process 1100 includesmeasuring 1110 a voltage level of a battery connected between terminalsof a rectifier; selecting 1120 a modulation scheme from among two ormore modulation schemes based on a measured voltage level of thebattery; and controlling 1130 a set of switches of the rectifier torectify a multilevel voltage signal on a transformer connected to therectifier using the selected modulation scheme. For example, the process1100 may be implemented by the system 1000 of FIG. 10. For example, theprocess 1100 may be implemented to control switches in a multilevelsynchronous rectifier and/or to control switches in a multilevelinverter. For example, the process 1100 may be implemented using thesystem 400 of FIG. 4. For example, the process 1100 may be implementedusing the system 700 of FIG. 7.

The process 1100 includes measuring 1110 a voltage level of a battery(e.g., a low voltage battery) connected between terminals of a rectifier(e.g., the rectifier of the system 400 or the rectifier of the system700). For example, a voltage sensor (e.g., a voltmeter) may be used tomeasure 1110 the voltage level of the battery. For example, the voltagelevel of the battery may vary as the battery is charged via therectifier and/or discharged by auxiliary systems.

The process 1100 includes selecting 1120 a modulation scheme from amongtwo or more modulation schemes based on a measured voltage level of thebattery. In some implementations, a first modulation scheme of the twoor more modulation schemes includes modulation states that individuallyutilize one at a time of a first secondary winding and a secondsecondary winding to conduct current through the battery, and a secondmodulation scheme of the two or more modulation schemes lacks modulationstates that individually utilize one at a time of the first secondarywinding and the second secondary winding to conduct current through thebattery. For example, the modulation scheme 500 of FIG. 5 may beselected 1120 when the measured battery voltage is near a high end of anoperating range of the battery (e.g., 60 volts) and the modulationscheme 600 of FIG. 6 may be selected 1120 when the measured batteryvoltage is near a low end of an operating range of the battery (e.g., 30volts). For example, the modulation scheme 800 of FIG. 8 may be selected1120 when the measured battery voltage is near a high end of anoperating range of the battery (e.g., 60 volts) and the modulationscheme 900 of FIG. 9 may be selected 1120 when the measured batteryvoltage is near a low end of an operating range of the battery (e.g., 30volts).

The process 1100 includes controlling 1130 a set of switches of therectifier to rectify a multilevel voltage signal on a transformerconnected to the rectifier using the selected modulation scheme. Forexample, process 1100 may be implemented with the system 400 and mayinclude controlling 1130 the first switch 430, the second switch 432,the third switch 434, the fourth switch 436, and the fifth switch 438 torectify a multilevel voltage signal on the transformer 410 using theselected modulation scheme (e.g., the modulation scheme 500 or themodulation scheme 600). For example, process 1100 may be implementedwith the system 700 and may include controlling 1130 the first switch730, the second switch 732, the third switch 734, the fourth switch 736,the fifth switch 737, and the sixth switch 738 to rectify a multilevelvoltage signal on the transformer 710 using the selected modulationscheme (e.g., the modulation scheme 800 or the modulation scheme 900).

The process 1100 may be repeated periodically to detect and respond tostate transitions of the battery voltage level (e.g., from a low voltagelevel to a high voltage level or from a high voltage level to a lowvoltage level) as they occur. For example, the process 1100 may berepeated once per minute, once per second, or once per millisecond.

A first implementation is a system that includes: a transformerincluding a first secondary winding, connecting a first tap and a secondtap, and a second secondary winding, connecting a third tap and thesecond tap; a first capacitor connecting the first tap to a first node;a second capacitor connecting the third tap to a second node; a firstswitch connecting the first node to a first terminal; a second switchconnecting the first node to the second node; a third switch connectingthe second node to a second terminal; a fourth switch connecting thesecond tap to the first terminal; a fifth switch connecting the secondtap to the second terminal; an electrical load connected between thefirst terminal and the second terminal; and a vehicle including apropulsion system configured to rotate wheels of the vehicle, a highvoltage battery configured to provide power to the propulsion system, aninverter connected between the high voltage battery and a primarywinding of the transformer, and a low voltage battery that is includedin the electrical load.

A second implementation is a system that includes: a transformerincluding a first secondary winding, connecting a first tap and a secondtap, and a second secondary winding, connecting a third tap and a fourthtap; a first switch connecting the first tap to a first terminal; asecond switch connecting the first tap to the fourth tap; a third switchconnecting the fourth tap to a second terminal; a fourth switchconnecting the second tap to the first terminal; a fifth switchconnecting the second tap to the third tap; a sixth switch connectingthe third tap to the second terminal; an electrical load connectedbetween the first terminal and the second terminal; and a vehicleincluding a propulsion system configured to rotate wheels of thevehicle, a high voltage battery configured to provide power to thepropulsion system, an inverter connected between the high voltagebattery and a primary winding of the transformer, and a low voltagebattery that is included in the electrical load.

A third implementation is a system that includes: a transformerincluding a first secondary winding and a second secondary winding; arectifier, including a set of switches, that connects taps of the firstsecondary winding and the second secondary winding to a first terminaland a second terminal, wherein the rectifier is symmetric with respectto the first secondary winding and the second secondary winding; abattery connected between the first terminal and the second terminal; aprocessing apparatus that is configured to control the set of switchesto rectify a multilevel voltage signal on the transformer, includingselecting a modulation scheme from among two or more modulation schemesbased on a measured voltage level of the battery; and a vehicleincluding a propulsion system configured to rotate wheels of thevehicle, a high voltage battery configured to provide power to thepropulsion system, an inverter connected between the high voltagebattery and a primary winding of the transformer, and wherein thebattery is a low voltage battery.

A fourth implementation is a system that includes: a transformerincluding a secondary winding connecting a first tap and a second tap; afirst capacitor connecting the first tap to a first node; a secondcapacitor connecting the second tap to a second node; a first switchconnecting the first node to a first terminal; a second switchconnecting the first node to the second node; a third switch connectingthe second node to a second terminal; and an electrical load connectedbetween the first terminal and the second terminal.

What is claimed is:
 1. A power converter comprising: a plurality ofswitching devices configured to be coupled between a plurality of ACvoltage terminals and a plurality of DC voltage terminals of the powerconverter, wherein the plurality of AC voltage terminals are configuredto be coupled to a plurality of secondary windings of a transformer; anda processing apparatus coupled to the plurality of switching devices andconfigured to operate the plurality of switching devices according to afirst modulation scheme responsive to a high voltage across the DCvoltage terminals and according to a second modulation scheme responsiveto a low voltage across the DC voltage terminals, wherein each of thefirst modulation scheme and the second modulation scheme is a periodicsequence of multiple modulation states with a period that corresponds toa whole number of periods of a multilevel voltage signal on thetransformer, wherein a modulation state specifies which of the pluralityof switching devices is in an on state, and wherein the first modulationscheme includes at least one modulation state that is different than themodulation states of the second modulation scheme.
 2. The powerconverter of claim 1 wherein the first modulation scheme simultaneouslyuses all of the plurality of secondary windings and the secondmodulation scheme alternately uses each of the plurality of secondarywindings.
 3. The power converter of claim 2 wherein at least one of thefirst and second modulation schemes includes first and second modulationstates corresponding to a same voltage level of a multilevel voltageacross the AC voltage terminals but activating different switchingdevices of the plurality of switching devices.
 4. The power converter ofclaim 3 wherein the processing apparatus is configured to invoke each ofthe first and second modulation states during a single period of themultilevel voltage.
 5. The power converter of claim 4 wherein theprocessing apparatus is configured to change a phase of each of thefirst and second modulation states between periods of the multilevelvoltage.
 6. The power converter of claim 1 wherein a first subset of theplurality of switching devices are switched identically in the first andsecond modulation schemes and wherein a second subset of the pluralityof switching devices are switched differently in the first and secondmodulation schemes.
 7. The power converter of claim 1 wherein at leastone of the first and second modulation schemes is configured tocommunicate power bidirectionally between the AC voltage terminals andthe DC voltage terminals.
 8. The power converter of claim 1 wherein: theplurality of secondary windings of the transformer comprise a firstsecondary winding coupled between a first AC voltage terminal and asecond AC voltage terminal of the plurality of AC voltage terminals anda second secondary winding coupled between the second AC voltageterminal and a third AC voltage terminal of the plurality of AC voltageterminals; and the plurality of switching devices comprise: a firstswitching device coupled between a first DC voltage terminal of theplurality of DC voltage terminals and the first AC voltage terminal; asecond switching device coupled between the first AC voltage terminaland the second AC voltage terminal; a third switching device coupledbetween a second DC voltage terminal of the plurality of DC voltageterminals and the third AC voltage terminal; a fourth switching devicecoupled between the first DC voltage terminal and the second AC voltageterminal; and a fifth switching device coupled between the second DCvoltage terminal and the second AC voltage terminal.
 9. The powerconverter of claim 8 wherein the first, second, and third switchingdevices are switched identically in the first and second modulationschemes and wherein the fourth and fifth switching devices are switcheddifferently in the first and second modulation schemes.
 10. The powerconverter of claim 1 wherein: the plurality of secondary windings of thetransformer comprise a first secondary winding coupled between a firstAC voltage terminal and a second AC voltage terminal of the plurality ofAC voltage terminals and a second secondary winding coupled between athird AC voltage terminal and a fourth AC voltage terminal of theplurality of AC voltage terminals; and the plurality of switchingdevices comprise: a first switching device coupled between a first DCvoltage terminal of the plurality of DC voltage terminals and the firstAC voltage terminal; a second switching device coupled between the firstAC voltage terminal and the fourth AC voltage terminal; a thirdswitching device coupled between a second DC voltage terminal of theplurality of DC voltage terminals and the fourth AC voltage terminal; afourth switching device coupled between the first DC voltage terminaland the second AC voltage terminal; and a fifth switching device coupledbetween the second DC voltage terminal and the third AC voltageterminal; and a sixth switching device coupled between the second ACvoltage terminal and the third AC voltage terminal.
 11. The powerconverter of claim 10 wherein the second and sixth switching devices areswitched identically in the first and second modulation schemes andwherein the first, third, fourth, and fifth switching devices areswitched differently in the first and second modulation schemes.
 12. Amethod of operating a power converter having a plurality of AC voltageterminals configured to be coupled to a plurality of transformersecondary windings and a plurality of DC voltage terminals, the methodcomprising: detecting a voltage across the plurality of DC voltageterminals; responsive to a high detected voltage, operating a pluralityof switches coupled between the DC voltage terminals and the pluralityof AC voltage terminals according to a first modulation scheme, whereinthe first modulation scheme simultaneously uses all of the plurality oftransformer secondary windings; and responsive to a low detectedvoltage, operating the plurality of switches according to a secondmodulation scheme, wherein the second modulation scheme alternately useseach of the plurality of transformer secondary windings, wherein each ofthe first modulation scheme and the second modulation scheme is aperiodic sequence of multiple modulation states with a period thatcorresponds to a whole number of periods of a multilevel voltage signalon a transformer including the plurality of transformer secondarywindings, wherein a modulation state specifies which of the plurality ofswitching devices is in an on state, and wherein the first modulationscheme includes at least one modulation state that is different than themodulation states of the second modulation scheme.
 13. The method ofclaim 12 wherein at least one of the first and second modulation schemesincludes first and second modulation states corresponding to a samevoltage level of a multilevel voltage across the AC voltage terminalsbut activating different switching devices of the plurality of switchingdevices.
 14. The method of claim 13, comprising: invoking each of thefirst and second modulation states during a single period of themultilevel voltage.
 15. The method of claim 14, comprising: changing aphase of each of the first and second modulation states between periodsof the multilevel voltage.
 16. The method of claim 12 wherein a firstsubset of the plurality of switching devices are switched identically inthe first and second modulation schemes and wherein a second subset ofthe plurality of switching devices are switched differently in the firstand second modulation schemes.
 17. The method of claim 12 wherein atleast one of the first and second modulation schemes is configured tocommunicate power bidirectionally between the AC voltage terminals andthe DC voltage terminals.
 18. An electronic device comprising: aplurality of AC voltage terminals coupled to a plurality of secondarywindings of a transformer; a plurality of DC voltage terminals coupledto a battery; a plurality of switching devices coupled between aplurality AC voltage terminals and a plurality of DC voltage terminals;and a processing apparatus coupled to the plurality of switching devicesand configured to operate the plurality of switching devices accordingto a first modulation scheme responsive to a high battery voltage andaccording to a second modulation scheme responsive to a low batteryvoltage, wherein the first modulation scheme simultaneously uses all ofthe plurality of secondary windings and the second modulation schemealternately uses each of the plurality of secondary windings, whereineach of the first modulation scheme and the second modulation scheme isa periodic sequence of multiple modulation states with a period thatcorresponds to a whole number of periods of a multilevel voltage signalon the transformer, wherein a modulation state specifies which of theplurality of switching devices is in an on state, and wherein the firstmodulation scheme includes at least one modulation state that isdifferent than the modulation states of the second modulation scheme.19. The electronic device of claim 18 wherein at least one of the firstand second modulation schemes includes first and second modulationstates corresponding to a same voltage level of a multilevel voltageacross the AC voltage terminals but activating different switchingdevices of the plurality of switching devices.
 20. The electronic deviceof claim 19 wherein the processing apparatus is configured to invokeeach of the first and second modulation states during a single period ofthe multilevel voltage.
 21. The electronic device of claim 20 whereinthe processing apparatus is configured to change a phase of each of thefirst and second modulation states between periods of the multilevelvoltage.